The present invention relates to a magnetostatic wave resonator using a principle such that a magnetic spin resonance of a thin magnetic film formed on a nonmagnetic substrate resonates in response to a microwave input signal.
A magnetostatic wave device obtained by working a YIG (yttrium, iron, garnet) thin film which was liquid phase epitaxial grown onto a GGG (gadolinium, gallium, garnet) nonmagnetic substrate into a desired shape has been disclosed in JP-A-62-245704 or the like as a device which is used in a microwave circuit or the like.
FIGS. 4A and 4B are schematic constructional diagrams of a magnetostatic wave device as an example shown in JP-A-62-245704. The magnetostatic wave device is constructed in the following manner. A YIG thin film 2 is formed onto a GGG substrate 1 by a liquid phase epitaxial method. A plurality of electrodes 3 made of gold or aluminum films are formed on the YIG thin film 2 by a photoetching technique so as to be arranged at regular intervals P. Terminals 4 (see FIG. 4B) made of gold or aluminum films are also formed on both sides of the electrodes 3 on the YIG thin film 2 by the photoetching technique. The magnetostatic wave device is connected at the terminals 4 to a part of a microwave circuit.
When a magnetic field H.sub.o is applied to the above magnetostatic wave device in parallel with or perpendicularly to the YIG film surface by either one of or both of a magnet and a coil (not shown), a resonance based on an electronic spin resonant phenomenon occurs. For instance, when an external magnetic field H.sub.o is applied as a perpendicular magnetic field onto the film surface of the magnetostatic wave device in FIGS. 4A, 4B, a magnetostatic forward volume wave is propagated in the YIG thin film and is reflected by both edge surfaces 5a and 5b of the YIG thin film and thereby becomes a standing wave, to produce resonance. The frequency at which resonance occurs can be changed by changing the magnetic field. A microwave oscillator can be manufactured by using such a magnetostatic wave device as a two-terminal device. It is well known that the magnetostatic wave device has excellent features such that it has a high degree of selection (Q) due to the YIG thin film being of a high quality, and a large variable width of the resonance frequency can be obtained, and the like.
A fact that the above device is relatively cheap because it is formed by the photoetching technique as also comparing with a device using a YIG sphere which has already widely been used in a microwave region is disclosed in JP-A-62-228802.
In FIGS. 4A and 4B, the positions of the electrodes 3 are shown at a pitch P of regular intervals. On the other hand, FIG. 5 shows positions of the electrodes in U.S. Pat. Ser. No. 4,782,312 as another conventional technique. FIG. 5 shows the case of a device having a length W and a width 1, where an input electrode 6a and an output electrode 6b are arranged at the peak positions of a Jth order resonance mode.
In FIG. 6A, J indicates a mode of a magnetostatic wave which stands in the width (i) direction of the electrode of the magnetostatic wave device. In this case, if the input electrode 6a and the output electrode 6b individually exist as shown in FIG. 5, the peak position in the lowest order resonance mode is J=2. Such a state corresponds to the positions of a and b in FIG. 6A. In the case of arranging a single electrode without separating the input and output electrodes, a position c corresponding to J=1 in the lowest order resonance mode is set.
However, in the above conventional technique, as shown in FIG. 6A, since high order modes other than the magnetostatic wave mode for coupling exist, a spurious resonance occurs due to the high order modes. For instance, in the case of constructing a microwave oscillator using such a resonator, there is a phenomenon such that an oscillation occurs at an undesirable frequency. Although an output of the main resonance is high even at the electrode positions in FIG. 5, the spurious resonance cannot be suppressed. Therefore, there is a problem such that an output of the undesirable frequency still remains.